Landscapes while wandering the planet
It is often hard to classify why the tub is green. Fresh travertine is bright white in color and as it weathers it changes to gray. Bright colored cyanobacteria and algae mats which were dependent upon a stable temperature and a flow of water also change as the microorganisms die creating a stark, bleak landscape. This one falls somewhere in between and can be assumed to be from algae mats.